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            <h2><font color="#FFFFFF">Directed Acyclic Graph </font></h2>
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<p>If you choose &quot;Directed Acyclic Graph,&quot; (DAG) you will be limited to constructing directed acyclic graphs.
    That is, you will only be allowed to constructed directed (--&gt;) edges, and you will not be permitted to construct
    cycles in your graph (X--&gt;...--&gt;X for some variable X in your graph).</p>
<p>To construct a DAG graph, place a Graph box on the workbench (see <a href="../../graph/graphs.html">Graphs</a>),
    double click the Graph box, choose &quot;Directed Acyclic Graph &quot; from the menu, and click &quot;OK.&quot; Once
    you click &quot;OK,&quot; you will be given a choice either to generate your own graph by hand or to have the
    program generate a graph for you with a specified number of variables, variable values, and directed edges:</p>
<p><img height="328" src="../../images/graph1structureeditor.gif" width="283"><br>
    <br>
    If you select &quot;Created manually&quot; and click &quot;OK,&quot; a blank graph editor window is opened. If you
    select &quot;A random DAG,&quot; you will need to fill in parameters to generate a random DAG. See <a
            href="../../graph/generating_random_dags.html">Generating
        Random DAGs</a> for more information.</p>
<p>You may at this point add variables and edges to the graph, or remove them if they're already there. To add a
    measured variable to the graph, click &quot;Add Variable&quot; and then click in the white workbench area where you
    want the measured variable to be located. To add a latent variable to the graph, click &quot;Add Latent&quot; and
    then click in the white workbench area where you want the latent variable to be located. The names of an added
    variable will be the first name in the sequence X1, X2, ..., that's not already in the graph. These names may be
    changed; see <a href="../../graph/advise_editing_node_properties.html">Editing Node Properties</a> for details. </p>
<p>To remove a variable from the graph, click on the variable you want to delete to select it and then press the delete
    key. If you remove a node from the graph, all of the edges attached to it will be removed as well. </p>
<p>To add an edge to the graph, click the type of edge you want to add, click and hold the mouse button down over the
    variable you want to edge to be from, and then drag the mouse to the variable you want the edge to be to. For a DAG,
    you are limited to one type of edge--viz., a directed edge (--&gt;). You are also prevented from forming cycles (X--&gt;...--&gt;X
    for some variable X). If you attempt to add an edge that would form a cycle, the edge simply won't be added. </p>
<p>To remove an edge from the graph, click on the edge you want to remove to select it and then press the delete
    key. </p>
<p>If all you want to do is change the directions of edges, there is a shortcut way to do this. Simply click on the
    endpoint of the edge you want the arrow to be on, and the edge will change direction for you. See <a
            href="../../graph/edge_orientation_shortchuts.html">Edge Orientation Shortcuts</a>.</p>
<p>A sample graph might look like this, after adding three variable and two edges: </p>
<p><img height="529" src="../../images/dageditorwindow.gif" width="540"></p>
<p>Once you have made a graph, you may rearrange the nodes by clicking and dragging; the edges will follow along so taht
    the structure of the graph remains the same. If you would like to move a whole section of nodes to another location,
    draw a &quot;rubberband&quot; around them and click on any one to move them. See <a
            href="../../common_tasks/selecting_groups_of_nodes.html">Selecting Groups of Nodes</a> for details. If you
    would like to change the name of a variable, or change whether the variable is latent or measured, double click the
    variable, edit its properties, and click &quot;OK.&quot; See <a
            href="../../graph/advise_editing_node_properties.html">Editing Node Properties</a> for details. </p>
<p>When you click &quot;Save,&quot; the graph editor window will close, and the contents will be saved in memory. If you
    click &quot;Cancel,&quot; the changes you made while editing will be disgarded, and the state of the graph before
    editing will remain unchanged. You may change the graph you made at any time by reopening the Graph box and adding
    or remove variables or edges or rearranging variables.</p>
<p>If you right click on the Graph box, a popup menu will appear with several options. See <a
        href="../../graph/popups.html">Popup Menus </a> for more detail.</p>
<p>&nbsp;</p>
<h3>Important Points. </h3>
<ol>
    <li>If you create a model with a latent variable, if you later use the model to generate data, values for the latent
        variables will not be shown. See <a href="../../graph/measured_vs_latent.html">Measured Vs. Latent Variables</a>.
    </li>
    <li>If you have introduced any boxes that depend on a Graph box, changing the graph will alter the contents of all
        boxes downstream in the flowchart from the Graph box. Often it is easier to simply create a new Graph box in the
        same main workspace window--there is no limit to how many graph or other boxes you can have at the same time.
        See<a href="../../graph/advise_flowchart_dependencies.html"> Flowchart Dependencies</a>.
    </li>
</ol>
<p>&nbsp;</p>
<h3><a name="possible_parents"></a>Possible Parents for &quot;Directed Acyclic Graph&quot; </h3>
<p> A &quot;Directed Acyclic Graph&quot; model can be self-standing, as described above. However, it can also be made a
    child of a number of other models of a variety of different box types. Usually what this does is to make a copy in
    the &quot;Directed Acyclic Graph&quot; box of a preexisting graph in the parent model, which is often a convenient
    thing to be able to do. The following models all have graphs that, if they happen to be DAGs, can be copied into a
    &quot;Directed Acyclic Graph&quot; model:</p>
<ol>
    <li>All graph models.</li>
    <li>All search models.</li>
    <li>All parametric models.</li>
    <li>All instantiated models.</li>
    <li>All updater models.</li>
</ol>
<p>In certain special cases, making a &quot;Directed Acyclic Graph&quot; model a child of another model has a
    specialized behavior. If you make a &quot;Directed Acyclic Graph&quot; model a child of a Data box model, the effect
    is to create a graph with all of the variables in the data set but no edges, as illustrated below.</p>
<p><img height="535" src="../../images/dag_from_data2.gif" width="561"></p>
<p>&nbsp;</p>
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